The process used at present for producing butyl rubber is known, for example see Ullmanns Encyclopedia of Industrial Chemistry, Vol. A 23, 1993, pages 288-295. The cationic copolymerization of isobutylene with isoprene in the slurry process and with methyl chloride as the process diluent is carried out at −95° C. using aluminum trichloride as an initiator activated by the addition of small amounts of water or hydrogen chloride. The low polymerization temperatures are necessary in order to achieve sufficiently high molecular weights for rubber applications.
The use of divinyl aromatic monomers, such as divinylbenzene (DVB), in the cationic polymerization of isobutylene and isoprene leads to the formation of crosslinked structures when both vinyl groups of the DVB molecules are reacted and incorporated into different polymer chains. The resulting isoolefin polymer therefore will have a certain amount of gel, i.e., a fraction insoluble in a hydrocarbon solvent such as cyclohexane. During crosslinking processes, a certain portion of divinylbenzene molecules reacts only partially. This happens when only one vinyl group of the crosslinking agent reacts and becomes chemically bound to a polymeric chain while the other vinyl group remains as an unreacted group in the chain. It was demonstrated (“Rubber Chem. Technol.”, 42 (1969) 1147-1154) that these so-called pendant vinyl groups are critical in imparting to such polymers curability with free radicals, e.g., from decomposition of peroxides. This feature distinguishes such polymers from regular butyl rubber or polyisobutylene, with the latter polymers decomposing under the action of peroxides.
The commercial terpolymer of isobutylene, isoprene and divinylbenzene, manufactured by Bayer Inc., is known under the name of XL-10000. Several of its applications are based on peroxide-induced cure of this specialty polymer. Presently, there is no method to steer the manufacturing process of this polymer with respect to controlling its composition that affects subsequent behavior during vulcanization with peroxides. The development of such a process control tool is very desirable. It could be used to tailor-make polymers with targeted curability for particular applications.